Co2 purity

[jerrylotto]

completley off topic but i just did what i assume is very poorly done molar math on 50ppm.....that would be like 2.5 grams of oxygen in a keg, which would probably be enough to mess up hops in a keg in a while. i just loosly did it and with my burst carbing by weight know that would be .06 mols of o2 compared to the co2, and then i burst with ~1.2oz...molar weight of o2 would be around 28 co2 44?

(my idea for a new homebrew device, an inline filter for scrubing co2! i'll make a killing selling replacement filter packs! )

20 PSI of CO2 gas, in a 5 gallon ball lock, weighs about 50 grams (1.76 ounces).
50 grams of CO2 is about 1.14 mol for the head space of an empty keg
50 ppm O2 would therefore be .000057 mol or .0018 grams or 6.35e-5 oz, not 2.5 grams!

If you then figure that you carbonate to about 2.5 vol of dissolved gas, your total O2 exposure would be 0.0045 grams O2 in the beer + an additional .0018 from the makeup head space or 0.0063 grams worst case (the last dregs).

 

[jerrylotto]

PS - CO2 purity levels by grade:

Grade	Purity
Research	99.999
Super-critical Fluid	99.998
Laser	99.95
Anaerobic	99.95
Beverage	99.9
Food	99.9
Bone Dry	99.8
Medical	99.5
Industrial	99.5

 

[Vale71]

But as I've said before, I have ROUTINELY watched levels in transferred beer (which is the on-label usage) drop below normal transfer pickup levels with application of CO2 via carb stone (gas stripping) using bulk supply (which we've measured to 5-8ppb) and rise using bottled CO2. If the supply were in the ppm range instead of ppb, I'd expect it to rise (or rise further), not fall. It gives me some confidence that even if those gas readings aren't 100% accurate they're close to it.

It just occurred to me that when measuring dissolved oxygen (or any other gas) the measurement is given in ppm or ppb mass/mass and not vol/vol. This would also be a reason why the instrument gives unrealistic readings when measuring a gas mixture that has a density much lower than that of water or finished beer. Even if the whole residual O2 (let's say it's really 50 ppm vol/vol) where to go into solution you would not reach 50 ppm mass/mass but rather something in the 10-100 ppb range. In other words the sensor probably gives valid readings of the O2 concentration but the instrument's logic is translating it into a measurement under a different assumption, i.e. an O2/water mixure instead of an O2/CO2 mixture.

 

[Broothru]

Hopefully they can use much more "dirty" (and cheap) CO2 sources for dry ice production.

Good point. And assuming the manufacturers of dry ice are rightly focused on not only on production but also economy, why should they? The level of oxygen 'contamination' in industrial CO2 isn't a factor in dry ice production, so why would they pay 10x as much for their raw material?

Brooo Brother

 

[Vale71]

Assuming that the instrument's sensor is correctly reading the concentration of O2 and then translating it in mass/mass dimensionless (assuming a density of 1000 kg/m^3) units your reading of 40ppb in the gas should then actually correspond to 28ppm which is totally believable for food-grade CO2 bought from a reputable supplier.